Radio frequencies (RF) have been used in various industries for a number of years. One common use of this type of energy is the household cooking appliance known as the microwave (MW) oven.
Microwave radiation couples with, or is absorbed by, non-symmetrical molecules or those which possess a dipole moment. In cooking applications, microwaves are absorbed by water present in food. Once this occurs, the water molecules rotate and generate heat. The remainder of the food is then heated through a conductive heating process.
Hydrocarbons do not typically couple well with MW radiation. This is due to the fact that these molecules do no possess a dipole moment. However, heavy crude oils are known to possess asphaltenes which are molecules with a range of chemical compositions. Asphaltenes are often characterized as polar, metal containing molecules. These traits make them exceptional candidates for coupling with microwave radiation. By targeting these molecules with MW/RF radiation, localized heat will be generated which will induce a viscosity reduction in the heavy oil. Through the conductive heating of the heavy crude oil or bitumen in place, a potential decrease in the startup time of a steam assisted gravity drainage (SAGD) operation may be experienced. This may also lead to decreases in the amount of water required and green house gas emissions produced which will have positive economic and environmental impacts on operations.
Additionally, the use of MW radiation in the presence of an alternate heat source can decrease the activation energy required for converting and breaking down carbon-carbon bonds. This synergistic effect can lead to the in situ upgrading of heavy crude oils by breaking down molecules which are known to significantly increase the viscosity of the crude oil. However, the use of RF/MW frequencies in a reservoir is not straight forward, nor is the selection of the appropriate RF/MW frequency.
U.S. Pat. No. 4,144,935 attempts to solve this problem by limiting the range in which radio frequencies are used to heat a particular volume in a formation. Such a method decreases the ability for one to use radio frequencies over a broad area and does not eliminate the problem of selecting the appropriate radio frequency to match the multitude of chemical components within the crude oil or bitumen. Furthermore, this method does not teach directing a radio frequency into a production well or bitumen formation to upgrade the heavy oil prior to the refinery process.
By using variable microwave frequency, one can tune the microwave frequency generated within the reservoir to one that interacts best with the dipole moment present within the hydrocarbons. However, previous work has shown that microwave radiation alone is not sufficient to break bonds, but the activation energy associated with breaking bonds is lowered when bonds are rotated in the presence of elevated temperatures.
U.S. Pat. No. 5,055,180 attempts to solve the problem of heating mass amounts of hydrocarbons by generating radio frequencies at differing frequency ranges. However use of varying radio frequencies means that there are radio frequencies generated that are not efficiently utilized. In such a method one would inherently generate radio frequencies that have no effect on the heavy oil or bitumen. Furthermore, this method does not teach directing a radio frequency into a production well to upgrade the heavy oil before transporting to the refinery.
There exists a need for an enhanced process that couples the use of microwave MW/RF radiation to produce an upgraded hydrocarbon within a production well within a bitumen or heavy oil formation.